In the field of refrigeration systems in air-conditioning apparatuses, there has been proposed one including a differential pressure-type throttle device instead of a capillary tube serving as the throttle device. For example, a differential pressure-type throttle device like those disclosed in patent document 1 to patent document 4 is configured to optimally control a pressure of a refrigerant between an outlet of a condenser and an inlet of an evaporator in order to efficiently operate a compressor in accordance with an outside air temperature. Moreover, in a refrigeration system capable of changing the number of revolutions of the compressor, the differential pressure-type throttle device is also configured to optimally control the pressure of the refrigerant according on the number of revolutions of the compressor from the labor saving point of view.
As shown in FIG. 1 of patent document 1, the differential pressure-type throttle device comprises: a cylinder provided at a ductwork that constitutes a refrigerant flow channel; a first valve body and a second valve body each provided with a valve portion and configured to open and close a valve seat in a passage inside the cylinder; a plurality of springs each configured to bias the valve portion of the corresponding one of the first and second valve bodies such that the valve portion of the first and second valve bodies establishes a closed state of the valve seat; shaft-like members each provided with a tapered portion located inside a contracted tube portion of the corresponding one of the first and second valve bodies, and designed to form a throttle flow channel between an inner edge portion of the contracted tube portion and the tapered portion; a plurality of stoppers each coming into contact with one end of the corresponding spring, and configured to adjust elastic forces of the plurality of springs; and setscrews fitted into female screw holes in the stoppers and configured to perform positioning of the shaft-like members in an axial direction.
In such a configuration, when a differential pressure between the front and back of the above-mentioned throttle flow channel corresponding to a designed pressure of the refrigerant falls below a predetermined value, the biasing forces of the springs is adjusted by the stoppers such that the valve portions of the first valve body and the second valve body establish the closed states of the corresponding valve seats. At that time, when the valve portions of the first valve body and the second valve body establish the closed states of the valve seats, the position of the corresponding shaft-like member is adjusted by one of the setscrews such that the size of the above-mentioned throttle flow channel becomes a predetermined size. Hereby, at the time of cooling, the refrigerant passing through the passage in the cylinder is reduced in pressure by the above-described throttle flow channel, and is discharged from the cylinder. On the other hand, when the differential pressure between the front and back of the above-mentioned throttle flow channel becomes equal to or above the predetermined value, the valve portion of the first valve body establishes an open state of the valve seat, whereby the greater part of the refrigerant is discharged from the cylinder through a clearance between the valve portion of the first valve body and an inner peripheral portion of the cylinder and through elongated holes in the corresponding stopper.